Hyperledger Fabric is a project incubated by the Linux Foundation under the Hyperledger umbrella of projects. Hyperledger is used to refer to a collection of open source enterprise blockchain projects, tools, and utilities. The Hyperledger initiative's main purpose is to enable the collaborative development of enterprise blockchain. It has seen major contributions from IBM, Intel, SAP Ariba, and other global enterprises.
Fabric is one of the oldest and most mature projects under Hyperledger. It is intended to be a platform for developing blockchain solutions with a modular architecture. It allows different platform features such as consensus mechanisms, certificate authorities, and identity services to be available as plug-and-play features. To achieve this, it implements containerization, making it suitable for modern enterprise IT systems. Unlike other blockchain platforms, it does not implement native assets, accounts, or an unspent transaction model, making it suitable for a plethora of applications.
Hyperledger Fabric implements chaincodes, which are similar to smart contracts. One of the most important features it implements is a concept called channels, which are essentially private ledgers with a fixed number of participant nodes. Only authorized nodes and organizations can access a channel. Nodes can be members of multiple channels, and chaincodes, policies, and certificate authorities can be used across multiple channels.
Hyperledger Fabric takes a unique approach to consensus. It runs a stand-alone orderer peer. The orderer peer gathers transactions and transmits new blocks of transactions to the network peers. The orderer leverages an ordering mechanism based on Kafka or Raft to order transactions and create blocks.
To submit transactions, peers first send a proposed transaction to a select few peers in the network, known as endorsement peers. These peers are determined during channel creation. If the transaction does not violate the endorsement peer's internal state, it "endorses" the transaction and sends it back to the node that sent the proposal. The initiating node then gathers these responses and broadcasts these with the endorsements to the orderer. It also sends a read and write set that has the initial and final values of the state after the transaction has been executed.
The orderer will collect these transactions and generate a new block. Fabric allows users to modify block size and block generation time. The newly created blocks are then sent back to the peer nodes by the orderer. The peer nodes will first add the block to their private copy of the ledger. Next, they will check the transactions inside the block to ensure that the read and write set is in line with the value in their local state database. After this check, they will update their local state database with the new values resulting from the transaction.